Bleaching systems that act by means of strong oxidizers are mostly used for brightening of teeth. Depending on the form of application, the concentrations lie between 10-35% peroxide. In particular, concentrated hydrogen peroxide solutions or carbamide peroxide are used. The action mechanism is based on oxidative decoloration of incorporated colorants. They have an aggressive effect on the oral mucosa, so the contact must absolutely be avoided. However, strong oxidizers also degrade structure-relevant proteins in the enamel. The content of natural macromolecules in dental enamel depends on the degree of maturation and is about 1-2 wt. % in adults. Proteins are preferably found on the surface of enamel prismatic units, but can also be integrated in the crystal structure. Composite systems of an inorganic mineral and organic components (preferably proteins and polysaccharides) are characteristics of biomineralization. The specific interaction leads to increased rupture strength. If the organic components are chemically removed, embrittlement must be reckoned with. Accessibility for contaminants, at least in the first days after treatment, is also increased during oxidative tooth brightening, and the sensitivity to pain is sometimes strongly increased. A fine pore system presumably becomes passable by oxidation of the biological matrix, which was previously filled by protein. Because of this, pain stimuli can be conducted more readily to the tooth nerve and undesired foreign substances can diffuse in better. This would explain why bleaching applications must often be repeated and treated teeth can be vulnerable to inflammation. Many bleaching systems function at low pH values, which can also lead to demineralization and entail additional weakening for the tooth. Topographic investigations on bleached human teeth show a detectable increase in natural porosity (cf. Bitter N. C. and Sanders J., L.: The effect of four bleaching agents on the enamel surface: A scanning electron microscopic study. Quintessence Int 1993, 24: 817-24). In addition, increased sensitivity to acid attack results. Although the hardness of the tooth shows no measurable reduction after the bleaching procedure, studies on bleached teeth demonstrate a distinct reduction in microhardness and intensified dissolution phenomena after simulated demineralization-remineralization cycles. The effect is somewhat reduced by providing fluoride, but weakening is not eliminated (cf. Attin T., Kocabiyik M., Buchalla W., Hanning C., Becker K.: Susceptibility of Enamel Surfaces to Demineralization after Application of Fluoridated Carbamide Peroxide Gels, Caries Res 2003: 37: 93-99). Another study demonstrates that the tensile strength and rupture strength of enamel diminishes by up to 30% after exposure to bleaching solutions (see: Cavalli, V. et al.: Effect of carbamide peroxide bleaching agents on tensile strength of human enamel. Dental Materials (2004) 20, 733-9). A pain study demonstrates that after treatment with 35% hydrogen peroxide solution, ⅔ of the patients reported moderate to severe pain, which lasted up to 48 hours after treatment (see Nathanson D., Parra C.: Bleaching vital teeth: A review and clinical study. Compend. Contin. Educ. Dent. 1987; 8(7): 490-7). The studies provide no clear indication of irreversible pulp damage, but in animal experiments, cases of massive inflammation, dentin resorption up to death of the pulp occurred after bleaching of vital dog teeth (see Nathanson, D.: Vital tooth bleaching: Sensitivity and Pulpal considerations, JADA, 128 (April 1997) 41-4). A prerequisite for conventional bleaching procedures, in each case, are healthy teeth. If hypersensitive teeth, exposed tooth necks or caries are present, bleaching can irreversibly damage the tooth nerve. It is also conceivable that damage from repeated bleaching can accumulate in healthy teeth.
In order to counteract the problem, attempts are made to fill exposed micropores by biomimetic remineralization, and also to apply an apatite protective layer. Since apatite, and especially fluorapatite, from pH 5 represents the thermodynamically most stable calcium phosphate, it can be easily demonstrated that, at physiological pH value, apatite is preferably formed in the presence of calcium and phosphate ions. To correspond to the composite nature of the biological model, mineralization occurs in the presence of an organic gel. This means that macromolecules are integrated in the apatite structure.